For the production of building structures having good thermal and sound control properties, mortars containing foamed polystyrene, cement and water are used, which are formed into building units either at the site of the construction or in a factory producing building materials. Such mortar is explained in the specification of GB 1 498 383.
Building units are produced from mortar containing polystyrene foam in such a manner that the mortar is poured into a mould, pressed, and if necessary, heat treated for instance under pressure. Then when the appropriate solidity is achieved, it is taken out of the mould and is allowed to stand in order to minimise the contraction tendency of such concrete containing polystyrene foam, hereinafter referred to as foam concrete. After a prescribed standing time, the building units so produced are formed into the desired size and form.
Such processing cannot be carried out at the site of construction because there the mortar cannot be pressed, heat treated and allowed to stand. If such mortar is poured into e.g. the permanent formwork during construction, problems may arise due to contraction.